Pulverizing system



M. FRISCH Dec. 7, 1943. I

PULVERIZING SYSTEM Filed Aug. 5, 1940 1 NVENTOR fiver/1v FE/SCH ATTORPatented Dec. 7, 1943 PULVERIZING SYSTEM Martin Frisch, New York, N. Y.,minor to Foster Wheeler Corporation, New York, N. Y.,' a oorporation ofNew York Application August 3, 1940, Serial No. 350,347

v 16 Claims. (Cl. 839) This invention relates to pulverizing systems andmore particularly pertains to systemsfor pulverizing fuel such as coal,and feeding the fuel to a zone of combustion such as the furnace oia'steam generator, or the like.

In systems of this character, the. fuel. after ordinarily carried by, a.single current of air Like characters of reference refer to the sameparts in the several views.

" Referring to the drawing, reference character having been pulverizedto the desired fineness is moving through a conduit directly to one or 4more fuel burners. This air is preheated tothe desired temperature andisilrst conducted under pressure to the pulveri'zing means, such as asingle ball mill, by an air duct, and the flow of air through this ductis controlled ordinarily by one or more dampers, the arrangementbeingsuch that when for any reason the burners or the mill are shut down, theflow of hot air to the 'mill will be,stopped, as otherwise, a seriousexplosion might occur. vHowever, where a pluralityof fuel-air streamsflow from the mill to the combustion zone,'it is desirable frequently tooperate with less than all these fuel-air streams. In thesecircumstances, it is necessary to maintain the flow of preheated air tothe mill so long as combustion is-maintained, but to discontinue .thesupply of preheated air to the mill as soon as combustion entirelyceases to avoid the possibility of explosion in the system.

The present invention provides improved means for controlling the flowofpreheatedair to .thepulverizer in pulverizing systems wherein -aplurality of fuel-air streams flow from the pulverizer to the combustionzone and for controlling these fuel-air streams in response to Y varyingoperating conditions and fluctuations in ,pulverizer outputrequirements.

The particular features and advantages of the invention will beunderstood from the following -dmcription when considered in connectionwith the accompanying drawing forming a part thereof, and in which:

Fig. lris a more or less diagrammatic view, partly in elevation andpartly in section, of a pulverlzing and fuelfeeding system embodying.the invention; f Fig. 2 is a diagrammatic view of the automatic controlmeans: g

Fig.- 3 is an enlarged elevational view of part of the'apparatus shownin Fig; 1;.

Fig. 4 is a'partial elevational and longitudinal sectional view of afurther part of the apparatus shown in Fig. 1, and

Fig. 5 is an elevational view of damper control means for controlling inpart the output-of the pulverizins means.

the conveyors l6 and I! to the interior of the to a separate burner orto separate burner' ll designates generally 'a ball mill pulverizercomprising a cylindrical shell II which contains the material to bepulverized and grinding balls of various sizes. The shell is supportedby hollow-trunnions i 2 and' I3 and is adaptedto be rotated about itshorizontal axis. In the form of the invention chosen for illustration,the

unground coal or other material, is introduced to the mill at both endsthrough feed conduits I4 and I5, which communicate with the hollow vHelical conveyors l6 and I1 within 7 trunnions. the trunnions, andconnected to the shell for rotation therewith, convey, the ungroundmate-' 1 rial-into the shell. .Air in sufllcient quantity andat theproper temperature is conducted to the mill through a main air duct l8and branch ducts l9 and which communicate with the interior of the shellat .both ends thereof by means of conduits 2| and 22 extending throughthe trunnions l2 and i3 respectively. As the material is pulverized, itis picked upby' the air currents flowing into the shell-and carried bythe'air from the shell in separate streams through each of the trunnions.to classifiers 23 and 24 wherein undesirablycoarse or. oversizeparticles of the' material are separated from the air streams,

dropout of the classifiers, and are returned by shell. The'materialwhich has been pulverized to the desired extent is borne by the airstreams through conduits 25 and 28 to a pair of similar exhaustersindividually designated A and B, which are driven byelectric motors 21and 28 respectively. It will be understood that each exhau'sterdischarges through a suitable conduit groups, which may be employed inthe firing of a single furnace or a plurality of separate.

furnaces. k Connected to exhauster A at points 29 and 30,

Q are pressure .tubes ti and 32 respectively, while connected to.exhauster B at points 33 and 34 are similar pressure tubes 35 and 38.The con- '-duits .25 and 28 are respectively connected to the exhaustersA and B through exhauster inlet elbows 31. and 38. In the elbow 31 is adamper 39 for controlling the flow of fuel to the exhauster, and themill output is controlled in part by regulation of this damper. As shownin the drawing, the damper 39 is in fully opened position. The positionof .the damper 39 may be adjusted to points between fully opened andfully closed positions, and maintained in any adjusted position in.response to variations in combustion requirements by suitable meansactuated either manually or automatically. One such means will bedescribed hereinafter. When the exhauster is shut down, or ceases tooperate normally due to emergency conditions, the dam automaticallycloses, thereby, shutting off completely the supply of fuel to theexhauster.

. The damper is held in the desired open position by-the adJusting meansreferred to, and lever ll which releases the damper from the adjustingmeans, is retained in the position to eflect the release of the damperby a latch 02 which engages the keeper l3 thereon and is actuated by asolenoid ll. In normal operation, the solenoid "II is deenergised andthe latch is positioned to hold the lever CI in the position shown inFla. 3 for an open position of the damper. Upon failure of the exhausterfor any reason, or upon normal shut down of the furnace ormill, thesolenoid II will be energised-and the latch I! willrrbe tripped torelease the damper so that it will-move to closed'position by gravity.An air inlet" is'provided in the elbow 31 which is controlled by adamper ll, and means are provided -to cause this damper ll to open whenthe damper it closes so that fresh air may be drawn intothe elbow andthe associated elements of the system to prevent explosions. Inlet elbowll of exhauster B -is similarly constructed and is provided with similardampers and control means. therefor. An emergency shut off damper l! isdisposed in the hot air duct ll "leading to the mill. nected to thisdamper is a lever II for manually Conmoving the damper to open position.Within the duct- II is a vertically inclined seat It for the damper whenit is in closed position. The damper is maintained in open position innormal operationby a latch ll controlled by a' solenoid ll and whichengages the keeper on the lever ll.

The arrangement is such that when the solenoid is deenergized,.the latchwill hold the damper in open position., but when the-solenoidlsenergisedthe latch will trip and the damper will move to closed positionby gravity, it being understood that the' .damper is of greaterweightthan the lever 43. -The hot air duct it is also provided with throttlingdampers 41 for maintaining the v desired suction'on the mill. Thesedamper may be nianuallyoperated by alever ll, or they may beautomatically controlled by a mill suction regulator, if desired.Connected to the hot air duct between theemergency shut off damper l2and the' throttlingdampers I! is a tempering air inlet duct 4!. Flow ofair at atmospheric temperature through the duct 49 into the duct II iscontrolled by a damper IO.

' In the present. system, where one mill supplies fuel to two exhaustersoperatingv in parallel, it

1 may be frequently desirable, or at times neceshauster is operating anduntil both exhausters are shut down, and when both exhausters are nolonger functioningthe damper automatically closes to cut off the flow ofhot air to the mill. Referring to Fig. 2, an exhauster controller II isconnected across theexhauster A by the pressure tubes SI and I2, and asimilar exhauster controller 5| is connected across exhauster B bythepressure tubes 38 and It. The exhauster contrgller 5| includes amercury sealed bell 52 and mercoid switches Hand 54 which are closed bydownward movement of the bell and opened by upward movement thereof, andexhauster controller 5| includes a similar mercury sealed bell 52' andsimilarly operated mercoid switches 53' and M. Shut down or failure ofeither exhauster will causepressure changes on the inlet anddischarge-sides of each .exhauster which will be transmitted to thecontroller connected to the exhauster. The mercoid switches 53, 54 and53', II which are all shown in open position, are connected to athree-phase electrical circuit a, b, c which is connected to a source ofpower. As-

suming that both exhausters' are operating, if ex-- close-open cycleupon downward movement of the bell 52,.with the result that the damper39 is caused to close by the momentary energization of the solenoid 0through lead 55 and contactor I. The switch," is arranged to move backto open position to prevent burning out of the coil so of solenoid ID.The switch II remains in closed position until the bell I2 movesupwardly. When exhauster B is shut down, the pressure changes resultingwill be transmitted to the controller 5|,

the bell 52' will move downwardly and the switches 53' and 64' will bemoved to closed po- I sition. .The switch-IV is mounted and actuated sothat it passes from open to closed to open position upon downwardmovement of the bell 52',

with the result that the solenoid M is momentarily energized throughlead It and contactor II and the damper I! is moved to closed position.The switch ll remains closed, andsince this switch is in series with theclosedswitch 54,

the hot air shut-off damper cir'cuitis closed so through lead 51' andcontactor 88, which enersizes the solenoid l6 and thus permits the'hotair shut-oilv damper 42 to close. As the damper l2 approaches closedposition, a limit switch 59 in lead ill is automatically tripped open byany suitanism. This opens the circuit to'solenoid 4i an?1 prevents buming out of the coil of the soleno y In starting the system, the severaldampers are opened manually and latched in open position. After normalpressure is attained in the controllers by operation of the exhausters,the bells l2 and 52 in the controllers will move up wardly and will openthe switches 54 and 54'. The limit switch 59 is then closed and thesystem will then operate normally with both exhausters functioning.

From the foregoing it will be perceived that with this arrangement,preheated air will continue'to be supplied to the pulverizing means solong [as any fuel-air mixture is flowingto the burners or to thecombustion zone or zones supplied by' the pulverizing means, but that assoon as the flow of fuel-air mixture is cut oil entirely for any reason,the supply of preheated air to the pulverizing means ,is also cut 01!;thereby avoiding any chance of an explosion in the mill or in thesystem. This arrangement includes 7| control of each fuel-air streamfrom the mill to able means, not shown, connected to and operated by thedamper 42 or its associated mechthe extent that upon failure or shutdown of any exhauster, that exhauster and the burners served therebywill be isolated from the mill by a cut- 7 of! damper such as damper 39in elbow 31 which is connected to the exhauster A, thus avoidingexplosion due to flame propagation to the mill.

The use of a plurality of exhausters with a single mill provides greaterflexibility oi control of the firing means and greater efllciency of opveration of the pulverizing system.

Manually operated means are shown ior regulating the position of thedamper 39. Thedamper is fixed to a shaft 95 (Fig. which extends beyondthe elbow in which the damper is mounted, and on the outerend portion ofthe shaft 33, a control arm 33 is mounted for freemovement with theshaft. Secured to the hub of arm 99 by bolts 31 is a clutch member 33hav ing a notch or recess 39 which is shaped to re- Iceive a roller dogll secured to the outer end of -a clutch member II which is pivoted tothe end of arm as is placed in the recess of the lifting cam 93 in orderthat the upward movement ofthe solenoid lever will cause damper ll toclose the auxiliary air opening 64. The cam 99 on solenoid lever 3| hasa contour such that when the lever is in the latched position shown inFig. 3; the clutch comprising the members 98 and "II. is engaged toconnect the damper adjusting damper shaft 93. A link. I! is pivoted atone end v to an intermediate point of member H and pivoted at its otherend to one .face of a circumferentially slotted collar I3 which isfreely slidable on shaft 95. oppositely disposed pins 14 on the innerforked legs 15 of a bell crank lever are received .in the slot in thecollar 13. The bell crank lever is pivotally mounted at 19 between 1 theforked ends of'a support 11 which is fixed to the elbow or to some.other stationary member.

The other arm 19 of the bell crank lever carries a roller 19 which iscontinually urged into engagement with a cam 99 or other part of thesolenoid lever 9|, uponwhich the cam is fixed,

by a spring 9| which is disposed between theouter endofarm I5 and astationary part. of the elbow orother part of the apparatus. Thesolenoid lever 6| is mounted on and is freely movable which is pivotallyconnected to a stationary member 86. Rotation of the wheel 92 in onediarm 33 to the damper, and when the solenoid lever is'in asubstantially vertical unl-atched position the clutch will be disengagedso that the damper will be free of adjusting arm 68 and will moveunderits own weight to closed position.

Accordingly, movement of the solenoid lever 3| 'i'romunlatched tolatched position will cause the bell crank lever comprising arms I! and19 to move in a counter-clockwise direction about pivot 13 which willmove collar I3 to the right, as seen in Fig. 5, and will cause clutchmember II to move into engagement with member 68. With the clutchengaged, damper 39 is moved to the desired initially adjusted positionby movement 0 the hand wheel". When the damper is to be closed for anyreason, solenoid 43 is energized, latch 92 is tripped to free it fromengagement with keeper 63, solenoid lever Si is released and moves in acounter-clockwise direction to a substantially vertical position, duringwhich movement of the lever cam 80 will cause clockwise movement of thebell crank lever about pivot I3,- thereby'sliding collar 13 on shaft "tothe left as seen in Fig. 5, and disengaging clutch member II from member99, so that the damper is freed from'the adjusting means and moves toclosed position underits own weight. During normal operation when thedamper is connected to the adjusting means, the damper may be moved toany'desired adjusting position between open and closed positions byproper movement of the hand wheel 92, thereby controlling the quantityoi fuel-air mixture flowing from the mill through the exhauster to theone or more burners to control the rate of firing of the burners and thefurnace temperature in consequence.

Each damper 39 is adjusted independently so that. the rate of tiring ofthe burners served by rection causes the rods to move into sleeve 93,

and rotation in the opposite direction causes the rods to move ouwardlyof the sleeve. thus causing the damper to move toward open and closedposition respectively at such times as roller dog -Ill engages theclutch member 98. A weighted arm 91 is fixed to the damper shaft OI tocounter balance the weight of the damper. The damper II which controlsthe air inlet 9, has a link 99' fixed to the damper shaft and pivotallyconnected to one end of an arm 99, the other end of which rests in arecess in a lifting 1 cam 99 on solenoidlever 9|.

In operation ofthe damper control mechanism; assuming that the damper 39is in closed position and the solenoid lever 9| is in a substantiallyvertical position, having been released by the energization of solenoidl9, to open the.

damper and to set the damper in the position initially desired, thesolenoid lever 9i is'moved in a clockwise direction until it is in theposition shown in Fig. 3 with the solenoid latch 92 eneach exhauster isindependently controlled.

1 Where the exhausters serve burners in different furnaces, the firingof the furnaces may be individually controlled. 7 A

In lieu'of the manually operated means disclosed for regulating theposition of each damper 39, automatic means may be employed. One

gaging the keeper 33 to retain the lever in the position shown. It willbe understood that the solenoid 49 is deenergized, and that the lowersuch means suitable for the purpose is disclosed in Heat Engineering,January, 1940, volume XV, number 1, pages 2 to 8, published by FosterWheeler Corporation, Broadway, New .York city. It will be understoodthat separate regulating means are employed for each damper 39.

It is to be understood that changes may be made in the'particular form,location and relative arrangement in the sev ral parts of the apparatusdisclosed without departing from the principles of the invention, whichis not to be limited .excepting'by the scope of the appended claims.

What is claimed is:

l. Pulverizing apparatus comprising a mill,

means for supplying to the mill material to be pulverized, means forsupplyin to the mill a medium for carrying a pulverized .material, meansfor withdrawing from themill a plurality of streams of said medium withentrained pulverized material, flow controlling means in each of saidstreams, and means for controlling the supply of said .medium to themill in response to the flow. of said streams from the mill andoperative to continue the flow of said medium to the mill so long .assaid flow from the mill continuesin any stream. 2. Pulverizing,apparatus comprising a mill, means for supplying to the mill material tobe pulverized, means for supplying to the mill a medium for carrying apulverized material, separate conduits connected to the mill throughinlet and discharge of each of said exhausters for controlling theoperation of the first-mentioned damperitdmaintain said damper inoperative pos'itioni toradmit the. medium tothe mill and each of-which astream of said medium and suspended pulverized material is withdrawnfrom the mill, means in each of, said conduits for varying the quantityof said medium and pul- -verized material withdrawn in each ,stream, an

Y =duits tocut, oil the, flow oi-jthe, medium to the mill only when nowin all of said conduits is discontinued.

3. Pulverizing apparatus comprising a mill, means for supplying 'to themill material to be pulverized, means for supplying to the mill a mediumioracarrying a pulverized material, sep- '"-arate -conduits connected tothe mill through each; 'which a stream of said medium and suspendedpulverized material is withdrawn from *the mill, means in each of saidconduits for vary- ,ing the quantity or said medium and pulverized,material withdrawn in each stream, an exhauster connected with eachconduit, means for controlling the ,supply of said medium to the mill,and-.tmeans operative in response to the differential-Tin the pressurebetween th inlet and discharge ,of each of said exhausters to actuatesaid controlling means so; a to maintain th controlling meanslnoperative position to admit the medium-to-themill and responsive to -areduction in saidpressure difierence betweenthe in-. let and dischargeof all of said exhausters to cut ofl the flow of the medium to the millonly when 1 flow in all of said conduits is discontinued.

4. Pulverizing apparatus comprising a mill, means for supplyingto themill material to be pulverized, a conduit for supplying to the mill a.medium for carrying a pulverized material, a i-iamper for controllingthe conduit, a plurality of separate conduits connected to the millthrough each of which a streamof said medium and suspended pulverizedmaterial is withdrawn from the mill, an exhauster connected with each oftion in said pressure diflerence between the inlet and discharge of eachof said exhausters. to cut on the flow of the stream in said conduits,and electrically actuated means operative in responseto the differencein pressure between the responsive to ,a reduction in said pressuredifference between the inlet and discharge of all of said exhausters tocut of! the flow 01. the medium to the mill when the ilow in all of saidconduit is discontinued.

5. Pulverizing apparatus comprising .a mill,

means for supplying to the mill material to be pulverized, means forsupplying to the mill a medium forcarrying a pulverized material,control meansior controlling the supply of said medium to the mill,separate conduits connected to the mill through each of which a stream01' said medium and suspended pulverized. material is withdrawn from thmill, an exhauster connected with each conduit, a damper for controllineeach conduit, means for regulating-the position of the damper in eachconduit to vary the quantity of medium and suspended pulverized materialflowing through the conduit, and means responsive to the flow of saidstreams through the separate conduits adapted to operate saidfirst-mentioned control means to cut off th flow of the medium to themill when flow from the mill in all of said separate conduits isdiscontinued.

' 6..Pulverizing apparatus comprising a mill, means for supplying to themill material to be pulverized, means for supplying to the mill a mediumfor carrying a pulverized material, con+ trol means for controlling thesupply of said medium to the mill, separate conduits connected to themill through each of which a stream of said medium and suspendedpulverized material is withdrawn from-the-mill, an exhauster con-'nected with each conduit, a damper for controlling each conduit, meansfor regulating the position of the damper in each conduit to vary thequantity of medium and suspended pulverize'd material flowing throughthe conduit, means for disconnectingthe regulating means from thedamperto permit the damper to move to closed position, and meansresponsive to the flow oi said streams through the separate conduitsadapted to operate said first-mentioned control means to cut oil theflow oithe medium to'th mil; when'all of said dampers are moved toclosed position and flow irom the mill' in-all the separate conduits isthereby discontinued.

7. Pulverizing apparatus comprising a mill, means for supplying to themill material to. be pulverized, a conduit for supplying to the mill 9.medium for carrying a. pulverized material, a damper for controlling theconduit, a plurality oi separate conduits connected to the mill througheach or which a stream of said medium'and suspended pulverized materialis withdrawn from the mill, an exhauster connected with each of saidplurality of conduits, a damper for each of said plurality of conduits,means for regulating the position of the damper in eachof said pluralityof conduits to vary the quantity or medium and suspended pulverizedmaterial flowing through the conduits, means for disconnecting theregulating means fromthe damper in' each of said plurality of conduitsto permit the damper to move to closed position, and means forcontrolling the damper in the conduit through which medium is suppliedto the mill operative to maintain said damper in an open position solong as at least one of said other dampers is openand to close saiddamperw-hen all oi said other dampers. are closed, 7

8; Pulverizing apparatus comprising a mill. meansior supplying to themill material to be pulverized, means for supplying to the mill a mediumfor carrying, ;a pulverized material, a. plurality of. means.forjcanslng said-med m to flovathrough nd out-oitl'iev mill in aplurality oi. streams :canyingmulverized material in. sus- .pensiommeansin cache! said treams iprvary ing the quantity or said'medillm andsuspended pulverized material withdrawn in. each stream,

and means for controlling the supplyof medium to'the millin response tothe flow of the streams irom said mill operativeto continue the flow ofthe position of the damperin each of said plurality of conduits to varythe quantity of medium and'suspended pulverized material flowing throughthe conduits, andmeans {or controlling the damper in the conduit throughwhich medium is supplied-to the mill operativ to maintain said'damperinan open position so long as at least one .oi-saidother dampers is openand to close said damper when all of said other dampers are closed.

10. Pulverizing apparatus comprising a mill, means for supplying to themill material to be pulverized, means for supplying to the mill a mediumfor carrying a pulverized material, a plurality of means forcausing saidmedium to flow through and out of the mill in a' plurality of streamscarrying pulverized materialin suspension, -flow controlling ,means .ineach oi. said streams-operative to 'cut oil the flow of .any

*streamlrom the mill when the flow of said streamdecreases, and meanstor controlling the s ply oi said medium to the mill in response to theflow of said streams-from the mill and operative to cut oil the flow oi.said medium to.

the mill when all flow from the mill stops.

11. Pulverizing apparatus comprising a mill, means for supplyin to themill material to be pulverized, means for supplying to themill a mediumfor carrying a pulverized material, control means for controlling thesupply of said medium to the mill, means for'withdrawing from the-mill aplurality of "streams or saidimedium with entrainedpulverizedunateriaLflow controlling means in each oi said streamsoperative to cut oil the flow '01 any stream from the millwhen the flowof said stream decreases, "and means responsive-to the flow of saidstreams means for supplying to the mill material to be 1 pulverized, aconduit for supplying to-the mill eachjoi which a stream' or, saidmedium'iand suspended pulverized material is withdrawn from the mill, anexhausterconnected with each of said plurality of conduits, a damper foreach of said plurality of conduits,,.ilow controlling means in each orsaid separatejconduits operative to cut off the flow or mediumandpulverized 3 material through any one of said s'ep'a'r'ate conduits whenthe f flow thereinYdecreasesQmeans for regulating theposition'oithedampei" in each of said plurality or conduits to" vary.the quantity of medium and SuspenGedZpulverizedmaterial flowing throughthe conduits, and me'ansffor controlling the damper in the conduitthrough which medium. is supplied to the mill operative to maintainsaiddamper in an open position so long as at least one of said other dampersis open and to close said damper when all of said other dampers areclosed.

' 13. Pulverizlng apparatus comprising a mill,

a medium for carrying a pulverizedmaterial, a damper for controlling theconduit. a plurality of separate conduits connected to the mill througheach of which a stream ofsaid medium and suspended pulverized materialis withdrawn from the mill, an exhauster connected with each of saidplurality of conduits, a damper for each duits at a point intermediatethe mill and the exhauster, and electrically actuated means operative inresponse to the diiierentialin the pressure between the inlet anddischarge 0! each of said exhausters for controlling the operation ofthe damper in each of the conduits through which said medium iswithdrawn from the mill to cut off the flow of the stream in any oneconduit when' the flow of said stream in that conduit decreases, andelectrically actuated means operativein response to the difierential inpres sure at the inlet and discharge of each of said exhausters forcontrolling the operation of the first-mentioned damper to cut oil theflow oi the medium to the mill when flow in all or said plurality ofconduits is discontinued.

. .14. Pulveri'zing apparatus comprising a mill,

means for supplying to the mill material to be pulverized, means forsupplyin to the mill a medium for carrying a-pulverized material,control means for controlling the supply or said mediumio the mill,means for withdrawing. from the mill aplurality oi streams. of. saidmedium with entrained'pulverized material, flow controls line means ineach of said streams, and electrically actuated means responsive to theflow of said streams from the mill adapted to operate thefirst-mentioned control means to cut oil the flow of the medium to themill when flow from the mill in all of said streams is discontinued.

15..Pulverizing apparatus comprising a mill,

. plying t 'the mill material to be irom the mill adapted to operatesaid flrst-men- I tioned control means to cut oilthe flow oi. the

medium to the mill when flow irom the mill in all of said streams stops.

l2. Pulverlzing apparatus comprising a mill, means for supplying '00 themill material to be pulverized, a conduit for supplying to the mill amedium for carrying a pulverized material, a damper for controlling theconduit, a plurality of separate conduits connected to the mill through75 trol means to cut oil the flow. oi the medium to pulverized, meansfor supplying to the mill a medium for carrying a pulverized material,control means for controlling the supply of said medium to the mill,means ior withdrawing from the mill a plurality of streams of saidmedium with entrained pulverized material, electrically actuated meansoperative in response to the flow of said streams from the mill forcontrolling the operation of the flow controlling means in each of saidstreams, and electrically actuated means responsive to the flow of saidstream from the mill adapted to operate the first-mentioned con- 01'said plurality of conduits for closing said constreams is discontinued.

16. Pulverizing apparatus comprising a mill, means for supplying to themill material to be pulverized, means for supplying to the mill a mediumfor carrying pulverized material, separate conduits connected to themill through each of which a stream oi. said medium and suspendedpulverized material is withdrawn from the mill, an exhauster connectedwith each conduit, flow controlling means in each or said conduitsresponsive to the diflerence in pressure produced by the exhausterconnected to the conduit and operative to maintain the flow controllingmeans in each 01' said conduits in operative position to permit the flow01 medium through said conduits and responsive to a reduction in saidpressure difierence between the inlet and discharge of each of saidexhausters to cut oil. the flow of the stream in said conduits, meansfor controlling the supply of said medium to the mill, and meansoperative in response to a difference in pressure produced by saidexhausters to actuate said means for controlling thesupply of saidmedium so as to maintain said means for controlling the Supp y of mediumin operative position to admit the medium to the mill and responsive to.a reduction in said pressure diflerences produced by the exhausters inall of said conduits to cut of! the flow oi the medium to the mill onlywhen flow in all of said conduits is discontinued.

Y MARTIN FRISCH.

